The present invention relates to a composition to enhance the rate of skin cell renewal or exfoliation and to a method of increasing the skin cell renewal rate. In particular, the present invention relates to a composition containing hydroxycarboxylic acid and an enhancing effective amount of oat extract. The present invention also relates to a method of increasing the rate of skin-cell renewal by applying a composition to the skin, wherein the composition comprises a hydroxycarboxylic acid and an enhancing effective amount of oat extract.
With the aging population, there is a continuing effort to provide cosmetic compositions to improve the appearance of the skin. Thus, many compositions are directed to improving the moisture retaining properties of the skin and consequently, include known moisturizers. At the same time, many consumers seek to use only natural ingredients. As a result, moisturizers such as oatmeal and related oat products have been incorporated into cosmetic compositions.
Recently, in addition to improving the moisture retaining properties of the skin, many compositions have included hydroxycarboxylic acids such as glycolic, lactic, citric, and malic acids in an effort to increase the exfoliation or desquamation of the outermost layer of skin. Thus, cosmetic compositions containing hydroxycarboxylic acids are being marketed for such uses as dry skin, the reduction of wrinkles and fine lines and to combat the effects of aging.
Human skin may be classified into two major parts: the outer layer or epidermis and an underlying layer or dermis. The dermis contains, among other things, blood vessels, nerves, collagen, elastin, and fibroblast cells, which are responsible for the biosynthesis of collagen and elastin.
The epidermis itself also may be considered to consist of two major zones, an inner or malpighian layer and an outer or horny layer. The malpighian layer, a living tissue, may be further divided into basal, spinous, and granular layers. The horny layer, a dead tissue, is also referred to as stratum corneum.
In the natural process, basal cells in the basal layer move outward through the spinous and granular layers to become dead cells called corneocytes, in the stratum comeum. The stratum corneum consists of approximately 14 layers of corneocytes. In the normal skin it takes about 14 days for the basal cells to move from the basal layer to the end of the granular layer and to become corneocytes, and another 14 days to reach the outermost layer of the stratum corneum, where they are naturally shed or exfoliated. This process of forming corneocytes is called keratinization, and stratum corneum are the natural products produced by this process. The stratum comeum is the skin tissue that one feels when touching the skin. Usually, it takes about 28 days for cells of the basal layer to move outward to the surface in the course of making new skin.
It is thought that by increasing the natural desquamation rate of the outermost part of the stratum corneum and thus exposing lower layers of the stratum corneum, the appearance of the skin will be improved. Many substances are known to increase the rate of natural desquamation but recently hydroxycarboxylic acids have received an increasing amount of attention. A drawback to the use of hydroxycarboxylic acids is that they can irritate the skin of the user. Thus, it would be desirable to incorporate a substance to reduce the possible irritating effect of the hydroxycarboxylic acid. It would also be desirable to increase the rate of desquamation beyond that provided by the hydroxycarboxylic acid without further increasing the possibility of skin irritation.